U.S. patent number 4,536,481 [Application Number 06/592,960] was granted by the patent office on 1985-08-20 for opal glasses having an apatite opacifying phase.
This patent grant is currently assigned to Corning Glass Works. Invention is credited to James E. Flannery, John L. Stempin, Dale R. Wexell.
United States Patent |
4,536,481 |
Flannery , et al. |
August 20, 1985 |
Opal glasses having an apatite opacifying phase
Abstract
This invention is directed to spontaneous opal glasses
containing an apatite opacifying phase and exhibiting a softening
point of at least 740.degree. C., excellent chemical durability,
and a temperature interval between the high temperature
crystallization liquidus and the emulsion liquidus greater than
50.degree. C. The glasses consist essentially, in weight percent on
the oxide basis, of
Inventors: |
Flannery; James E. (Corning,
NY), Stempin; John L. (Beaver Dams, NY), Wexell; Dale
R. (Corning, NY) |
Assignee: |
Corning Glass Works (Corning,
NY)
|
Family
ID: |
24372762 |
Appl.
No.: |
06/592,960 |
Filed: |
March 23, 1984 |
Current U.S.
Class: |
501/32; 501/59;
501/61 |
Current CPC
Class: |
C03C
3/097 (20130101); C03C 4/005 (20130101); C03C
3/118 (20130101) |
Current International
Class: |
C03C
3/118 (20060101); C03C 4/00 (20060101); C03C
3/097 (20060101); C03C 3/076 (20060101); C03C
003/08 (); C03C 003/10 (); C03C 003/30 () |
Field of
Search: |
;501/32,59,61,62,63 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
2394502 |
February 1946 |
Weyl et al. |
4298390 |
November 1981 |
Flannery et al. |
|
Foreign Patent Documents
Primary Examiner: Bell; Mark L.
Attorney, Agent or Firm: Janes, Jr.; C. S.
Claims
We claim:
1. A spontaneous opal glass exhibiting a dense white appearance, a
softening point of at least 740.degree. C., excellent chemical
durability, a temperature interval between the high temperature
crystallization liquidus and the emulsion liquids greater than
50.degree. C., and containing as the predominant crystal phase a
member selected from the group of Ca.sub.5 F(PO.sub.4).sub.3,
Sr.sub.5 F(PO.sub.4).sub.3, Ba.sub.5 F(PO.sub.4).sub.3, (Ca.sub.5-x
Ba.sub.x)F(PO.sub.4).sub.3 solid solution, (Sr.sub.5-x
Ba.sub.x)F(PO.sub.4).sub.3 solid solution, (Ca.sub.5-x
Sr.sub.x)F(PO.sub.4).sub.3 solid solution, (Sr.sub.5-x
Ca.sub.x)F(PO.sub.4).sub.3 solid solution, (Ba.sub.5-x
Ca.sub.x)F(PO.sub.4).sub.3 solid solution, and (Ba.sub.5-x
Sr.sub.x)F(PO.sub.4).sub.3 solid solution, said glass consisting
essentially, expressed in terms of weight percent on the oxide
basis, of
2. A spontaneous opal glass according to claim 1 containing 3-4%
PbO.
3. A spontaneous opal glass according to claim 1 wherein Na.sub.2
O+K.sub.2 O<13%.
Description
BACKGROUND OF THE INVENTION
Our U.S. Pat. No. 4,298,390 discloses the production of spontaneous
opal glasses wherein the opacity is the result of crystallinity in
the glass and Ba.sub.2 F(PO.sub.4) constitutes the predominant
crystal phase. Those glasses are asserted to manifest softening
points in excess of 710.degree. C., a white opacity, excellent
chemical durability, and to consist essentially, expressed in terms
of weight percent on the oxide basis, of 6-10% Na.sub.2 O, 1-6%
K.sub.2 O, 4-11% BaO, 9-18% Al.sub.2 O.sub.3, 1-5% B.sub.2 O.sub.3,
50-70% SiO.sub.2, 3.5-7% P.sub.2 O.sub.5, 1-4% F, and optionally up
to 3.5% CaO and/or up to 5% total of MgO and/or SrO.
The patent explains that those glasses are characterized by a
two-stage liquidus phenomenon; viz., a high temperature cloudiness
or opacification, termed an emulsion liquidus or liquid-liquid
phase separation, and the normal crystalline opal liquidus.
Analysis of the phase separation found it to be rich in Na.sub.2 O,
BaO, P.sub.2 O.sub.5, and F. X-ray diffraction analysis of the
crystalline opal phase identified the predominant crystal phase to
be of a Ba.sub.2 (OH)PO.sub.4 type. Nonetheless, because X-ray
analysis does not distinguish between fluoride and OH, it was
assumed that fluoride substituted for OH in the crystal, thereby
leading to the crystals being described as Ba.sub.2 F(PO.sub.4).
Minor amounts of NaBaPO.sub.4 and other unidentifiable species were
also detected.
Culinary ware and tableware are thermally tempered to improve the
mechanical strength and thermal shock resistance thereof.
Unfortunately, breakage of such ware produced according to the
disclosure of U.S. Pat. No. 4,298,390 was not infrequently
experienced during the thermal tempering procedure. Microscopic
examination of the crystal phase indicated that a substantial
number of the crystals attained relatively large dimensions with
inclusions of such crystals exhibiting diameters in excess of
0.001" (.about.25 microns). Ware containing such large inclusions
do not survive the thermal shock inherent in the air chill
tempering process, viz., about 800.degree. C. to room
temperature.
A further and very extensive investigation of those glasses has
determined that the crystallization mechanism is more complex than
originally conjectured. This study demonstrated that, instead of a
single crystallization liquidus, as discussed in U.S. Pat. No.
4,298,390, there appears to be a first or high temperature
crystallization liquidus and a second or low temperature
crystallization liquidus. Hence, at the high temperature
crystallization liquidus at least one species of apatite-type
crystal [classical formula Ca.sub.10 F.sub.2 (PO.sub.4).sub.6 ]
precipitates out of the molten glass, and at the low temperature
crystallization liquidus at least one other species of apatite-type
crystal is generated, as confirmed by X-ray diffraction data. Much
solid solution is possible in the apatite structure which manifests
itself in very minor changes in the X-ray diffraction pattern;
i.e., the overall pattern is relatively indistinguishable from the
general appearance of classical apatite. Hence, as used herein,
apatite includes such solid solution crystals.
It was noted in U.S. Pat. No. 4,298,390 that the emulsion liquidus
and crystallization opal liquidus data were obtained utilizing a
hot stage microscope composite apparatus. Such apparatus relies
upon the sensitivity of the eye of the observer and, therefore,
involves a significant measure of subjectivity in the reported
determinations. Accordingly, to remove the element of subjectivity,
the emulsion and low temperature crystallization liquidi were
determined on a number of the working examples of the patent
employing laser reflectance measurements, that technique being
founded in conventional laser reflectance spectroscopy. Thus, those
liquidi are readily gained from laser reflectance or back
scattering/temperature curves. The high temperature crystallization
liquidus cannot normally be directly obtained from such curves
because that deflection is hidden in the steep slope brought about
by the emulsion phenomenon. Consequently, the high temperature
crystallization liquidus is read from the laser reflectance or back
scattering/temperature curve in the derivative mode.
Table A records the emulsion, high temperature crystallization, and
low temperature crystallization liquidi (in .degree.C.) measured on
several of the working examples provided in Table I of the patent.
The Example Nos. reflect those in Table I of the patent.
TABLE A
__________________________________________________________________________
1 2 3 7 8 9 10 12 15 17 18
__________________________________________________________________________
Emulsion Liquidus 1380 1400 1390 1380 1380 1370 1395 1380 1390 1400
1385 High Temp. Liquidus 1350 1365 1370 1350 1345 1345 1360 1350
1375 1370 1360 Low Temp. Liquidus 875 860 610 700 760 725 710 820
900 740 770
__________________________________________________________________________
As can be observed, the interval between the emulsion liquidus and
the high temperature crystallization liquidus is less than
50.degree. C., often no more than 25.degree. C. The above-mentioned
extensive investigation of those glasses has indicated that, to
prevent the formation of those large crystalline inclusions which
can cause mechanical breakage of ware, the temperature range
between the emulsion liquidus and high temperature crystallization
liquidus must be expanded. That is the principal objective of the
present invention.
SUMMARY OF THE INVENTION
We have found that the incorporation of about 2-12% by weight PbO
to compositions similar to those disclosed in U.S. Pat. No.
4,298,390 can substantially eliminate the above-described large
inclusions of apatite crystals while retaining the chemical and
physical properties of those glasses. PbO significantly lowers the
high temperature crystallization liquidus such that the interval
between the high temperature crystallization and emulsion liquidi
is expanded by at least 25.degree. C. and, frequently, in excess of
50.degree. C. Thus, the crystallization liquidus is generally
reduced to 1325.degree. C. and below. The emulsion liquidus will
generally remain essentially invariant with PbO contents up to
about 4%. At higher values the emulsion liquidus will be depressed
to some extent, but the reduction in the high temperature
crystallization liquidus will generally track that decrease, such
that the degree of expansion in the interval between the liquidi
will be maintained. Hence, rather than a spread of no more than
about 50.degree. C. and often no more than 25.degree. C. between
the liquidi, the addition of PbO opens the interval to greater than
50.degree. C., usually at least 75.degree. C., and occasionally in
excess of 100.degree. C. This enlargement in the range of
temperature between the crystallization and emulsion liquidi means
that the exposure of the glass to a temperature between those
liquidi, which is mandatory for dense opacification, can be
conducted at temperatures sufficiently above the high temperature
crystallization liquidus to minimize nucleation and the subsequent
growth of large crystalline inclusions.
The glasses of the instant invention exhibit softening points in
excess of 740.degree. C., excellent chemical durability, low values
of heavy metal release, and consist essentially, expressed in terms
of weight percent on the oxide basis, of:
______________________________________ SiO.sub.2 50-63 Na.sub.2 O
5.5-10 Al.sub.2 O.sub.3 10-14 K.sub.2 O 0-10 P.sub.2 O.sub.5 3.5-7
BaO 0-10 PbO 2-12 CaO 0-2.5 B.sub.2 O.sub.3 1-4 SrO 0-8 F 1.5-4
______________________________________ BaO + CaO + SrO at least 3
mole %
At least one member of the group CaO, SrO, and BaO must be present
to yield an apatite opacifying phase selected from the group of
Ca.sub.5 F(PO.sub.4).sub.3, Sr.sub.5 F(PO.sub.4).sub.3, Ba.sub.5
F(PO.sub.4).sub.3, (Ca.sub.5-x Ba.sub.x)F(PO.sub.4).sub.3 solid
solution, (Sr.sub.5-x Ba.sub.x)F(PO.sub.4).sub.3 solid solution,
(Sr.sub.5-x Ba.sub.x)F(PO.sub.4).sub.3 solid solution, (Ca.sub.5-x
Sr.sub.x)F(PO.sub.4).sub.3 solid solution, (Ba.sub.5-x
Ca.sub.x)F(PO.sub.4).sub.3 solid solution, and (Ba.sub.5-x
Sr.sub.x)F(PO.sub.4).sub.3 solid solution. All of those crystal
species have the apatite structure with the general formula R.sub.5
X(PO.sub.4).sub.3, wherein R is selected from the group of Ca, Sr,
and Ba, and X is selected from the group of F.sup.- and OH.sup.-.
The minimum level required for each or a combination of two or more
is expressed in terms of mole percent because of the obvious
differences in the molecular weights of CaO, SrO, and BaO. The
minimum quantities of CaO, SrO, and BaO necessary to achieve dense
opacity, approximated in terms of weight percent, are about 1%, 2%,
and 3%, respectively.
Scanning electron microscopy and X-ray emission data indicate that
lead enters the separated phase to inhibit thereby the formation of
the calcium and/or strontium and/or barium apatite crystals. Thus,
here again is support for the suggestion that lead enters into the
apatite phase to form an apatite solid solution containing lead
and/or a lead apatite phase, viz. Pb.sub.5 F(PO.sub.4).sub.3.
The most preferred levels of PbO to insure dense opacity, to
minimize heavy metal release, to maintain the softening point above
760.degree. C. to permit decorating with durable, high temperature
glazes and enamels, to exhibit excellent resistance to attack by
acids and bases, and to display extremely good detergent durability
will comprise about 3-4%. Whereas PbO contents up to 12% are
operable, the products resulting from those values do not manifest
any substantial improvement in properties and the softening point
may be reduced and chemical durability deleteriously affected.
Opacity is also generally affected adversely. Quantities greater
than 12% invariably result in reduced chemical durability and
increased heavy metal release.
Each of the remaining base glass constituents will be constrained
within the above-defined limits. For example, when the amount of
CaO exceeds 2.5%, PbO becomes ineffective in controlling the size
of the crystalline inclusions because of the great insolubility of
calcium apatite under those conditions. Above 8% SrO the glasses
display high emulsion liquidi with subsequent inclusion problems.
BaO levels greater than 10% cause the coefficient of thermal
expansion of the glass to become so high as to prevent satisfactory
thermal tempering. At P.sub.2 O.sub.5 levels below 3.5%, opacity
becomes poor and where P.sub.2 O.sub.5 is present in amounts
greater than about 5, PbO cannot be counted upon to always control
the growth of apatite inclusions. At least 1.5% F is necessary to
form the desired fluorapatite structure, but quantities greater
than 4% cause a decrease in opacity because the fluoride
solubilizes the components of the apatite phase in the melt. About
1.8-2.2% F is preferred. The total Na.sub.2 O+K.sub.2 O will
preferably not exceed about 13% since their fluxing action
solubilizes the crystal components which leads to reduced opacity.
K.sub.2 O is preferably present since its absence frequently
results in a glass having an undesirably high emulsion
liquidus.
PbO when present in the defined amounts of 2-12% in the inventive
opal glass system will, without fail, reduce the size of the
crystalline inclusions, but may not always totally eliminate them
at the higher levels of CaO, SrO, BaO, and P.sub.2 O.sub.5.
Al.sub.2 O.sub.3 contents should be maintained between 10-14% to
impart excellent detergent durability. Amounts in excess of 14%
customarily lead to a decreased emulsion liquidus and reduced
opacity. Where the B.sub.2 O.sub.3 level is below 1%, the emulsion
liquidus rises dramatically. On the other hand, contents of B.sub.2
O.sub.3 greater than 4% produce non-crystalline fluorphosphate opal
glasses of only medium opacity at best.
MgO and ZnO may form part of the glass composition in amounts not
exceeding 2.5% by weight total. A combination of PbO with ZnO
appears to enhance the inclusion-controlling capability of ZnO.
Nevertheless, when the content of ZnO exceeds two mole percent,
additions of PbO up to about 12% often result in a decrease of
opacity.
In summary, PbO in the apatite opal glass compositions of the
instant invention operates in accordance with the following
factors:
(a) it can essentially eliminate the undesirable large apatite
inclusions; i.e., it lowers the temperature for the appearance of
inclusions (high temperature crystallization liquidus); and
(b) it can maintain or lower the emulsion liquidus while expanding
the temperature interval between the high temperature
crystallization and emulsion liquidi; and
(c) it can increase the rate at which the emulsion and
crystallization phenomena occur.
It will be appreciated, of course, that conventional glass coloring
transition metal oxides and/or rare earth metal oxides may, if
desired, be incorporated into the glass compositions in the
customary proportions.
RELATED APPLICATION
Ser. No. 592,929, filed concurrently by us under the same title as
the instant application, discloses that the incorporation of ZnO in
compositions similar to those of U.S. Pat. No. 4,298,390 and
similar to those of the instant application can eliminate the large
crystalline inclusions in like manner to the action of PbO.
PRIOR ART
U.S. Pat. No. 4,298,390 provides an extensive recital of U.S.
patents having some relevance to spontaneous fluorophosphate opal
glasses and two other U.S. patents were cited during the
prosecution of the application maturing into that patent. Rather
than repeating that recital, however, the text of the patent is
explicitly incorporated herein by reference. Whereas none of the
patents reported therein or cited during the prosecution thereof is
as pertinent to the present disclosure as U.S. Pat. No. 4,298,390,
the instant invention being an improvement upon the latter, U.S.
Pat. No. 2,394,502 will be reviewed inasmuch as it discloses the
production of opal glasses containing a fluorapatite crystalline
opal phase.
That patent describes opal glasses having base compositions
consisting essentially, in weight percent, of:
______________________________________ SiO.sub.2 54-66 PbO 0-5
Al.sub.2 O.sub.3 0-6 B.sub.2 O.sub.3 0-50 Na.sub.2 O + K.sub.2 O
12-17 As.sub.2 O.sub.3 0-1 CaO 0-12 P.sub.2 O.sub.5 4-9 BaO 0-4 F
2.5-5 ______________________________________
No minimum quantity of CaO+BaO+PbO is specified, although it is
noted that at least one of the three must be present to participate
in the formation of the fluorapatite crystals. CaO is the preferred
oxide. It is stated that BaO and PbO reduce crystal formation
growth.
The maximum Al.sub.2 O.sub.3 content is considerably below that
required in the present inventive composition. Furthermore, BaO is
stated to adversely affect crystal formation such that the maximum
that can be tolerated is 4%. In contrast, the formation of crystals
is not adversely affected by BaO in the present composition, and
the minimum demanded to achieve dense opacity is about 3%.
DESCRIPTION OF PREFERRED EMBODIMENTS
Table I records exemplary compositions, expressed in terms of parts
by weight on the oxide basis, illustrating the compositional
parameters of the inventive glasses. Because the sum of the
individual components totals or very closely approximates 100, for
all practical purposes the values tabulated may be considered to
represent the compositions in terms of weight percent. Furthermore,
inasmuch as it is not known with which cation(s) the fluoride is
combined, it is simply recited as fluoride (F), in accordance with
conventional glass analysis practice. Commonly, about 20-30% by
weight of the fluoride will be lost through volatilization during
melting of the batch. Where desired, an oxide of arsenic or a
chloride salt may be included in the batch to perform its
conventional function as a fining agent. Table IA lists the
components of the several glasses in terms of approximate mole
percent.
The actual batch components may comprise any ingredients, either
the oxides or other compounds, which, when melted together, will be
converted into the desired oxide in the proper proportions. The
fluoride will typically be added as a silicofluoride. Whereas the
description below is based upon laboratory scale melting, it must
be recognized that the tabulated compositions would also be useful
in large scale commercial melting units.
The batch ingredients were compounded, tumble mixed together to
assist in obtaining a homogeneous melt, and charged into platinum
crucibles. The crucibles were introduced into a furnace operating
at about 1500.degree. C. and the batches melted for about four
hours. The melts were poured into steel molds to yield slabs having
the dimensions of 3.5".times.2.5".times.0.25", and the glass slabs
immediately transferred to an annealer operating at
500.degree.-550.degree. C., the slabs being cooled to room
temperature at a rate of about 50.degree. C./hour.
Table I also reports visual appraisal of the density of the opacity
(Opac.), the presence of inclusions (Incls.) in the slabs, and the
identity of the crystal phase(s) present (Cryst.) as determined via
X-ray diffraction data, listed in the order of extent present.
TABLE I 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24 SiO.sub.2 58.75 56.9 55.5 56.3 58.1 56.35 54.7 51.7 59.4 58.6
57.2 59.35 58.0 58.2 58.0 57.8 55.6 56.5 58.9 57.85 58.6 57.3 58.8
57.6 Al.sub.2 O.sub.3 15.4 14.95 14.6 14.8 12.8 12.4 12.1 11.4 13.2
12.9 12.6 13.1 12.9 12.8 12.8 12.7 12.25 13.0 13.0 12.7 12.9 12.6
12.9 12.7 CaO 4.05 3.1 2.3 0.8 1.55 1.5 1.5 1.4 1.7 0.8 -- 1.6 1.6
1.55 0.8 -- -- 1.7 1.6 1.55 1.6 1.55 1.6 1.55 BaO -- -- -- -- 6.4
6.2 6.0 5.7 6.7 6.45 6.3 4.35 2.2 -- 4.3 2.15 -- 6.2 6.5 6.4 6.45
6.3 6.5 6.35 Na.sub.2 O 8.5 8.3 8 .1 8.2 8.2 7.95 7.7 7.3 8.7 8.3
8.1 8.4 8.3 8.2 8.2 8.2 7.9 7.5 8.3 8.2 7.4 6.4 7.8 7.3 K.sub.2 O
1.95 1.9 1.85 1.9 3.3 3.2 3.1 2.9 -- 3.3 3.25 3.35 3.3 3.3 3.3 3.3
3.15 -- 2.0 0.65 3.3 3.25 2.65 1.95 P.sub.2 O.sub.5 4.5 4.3 4.25
4.3 4.15 4.0 3.9 3.7 4.3 4.2 4.1 4.25 4.2 4.15 4.15 4.15 4.0 4.1
4.2 4.15 4.2 4.1 4.2 4.1 B.sub.2 O.sub.3 3.45 3.3 3.3 3.3 2.4 2.35
2.3 2.15 2.7 2.45 2.4 2.5 2.45 2.4 2.4 2.4 2.3 2.5 2.45 2.4 2.45
2.4 2.45 2.4 PbO 3.35 6.5 9.5 9.6 3.1 6.0 8.8 13.8 3.2 3.1 6.1 3.2
6.3 9.3 6.2 9.3 14.9 6.1 3.15 6.2 3.15 6.1 3.15 6.15 F 2.28 2.2
2.15 2.18 2.12 2.05 1.99 1.9 2.2 2.1 2.1 2.2 2.15 2.1 2.1 2.1 2.0
2.3 2.15 2.1 2.15 2.1 2.15 2.1 MgO 0.9 0.87 0.85 0.86 -- -- Incls.
No No No No No No No No No No No No No No No No No Few No No No No
No No Opac. Medi- Medi- Very Poor Dense Dense Dense Dense Dense
Medi- Poor Poor Medi- Medi- Medi- Poor Poor Very Very Very Very
Very Dense Very um um Dense um um um um Dense Dense Dense Dense
Dense Dense Dense Cryst. -- -- Apatite -- Apatite -- -- Apatite
Apatite -- -- -- Apatite -- Apatite -- -- Apatite Apatite Apatite
Apatite Apatite -- Apatite 25 26 27 28 29 30 31 32 33 34 35 36 37
38 39 40 41 42 43 44 SiO.sub.2 59.9 58.55 57.25 59.3 58.0 58.0 58.2
59.15 57.5 58.7 56.85 58.2 56.3 54.9 57.5 55.6 53.65 57.0 53.0
58.25 Al.sub.2 O.sub.3 13.2 12.9 12.6 13.0 12.75 12.75 12.8 13.0
12.65 12.9 12.5 12.9 12.5 12.15 12.75 13.6 13.75 13.3 13.7 12.8 CaO
1.45 1.3 1.1 1.6 1.55 1.4 1.4 1.6 1.55 1.6 1.5 1.2 0.4 -- 1.55 1.5
1.45 1.55 1.45 1.55 BaO 6.6 6.45 6.3 6.5 6.4 5.1 5.85 5.4 3.2 6.5
6.3 5.4 3.15 -- -- 6.1 5.9 6.3 5.9 -- Na.sub.2 O 6.85 6.0 5.2 6.35
5.5 7.25 7.5 8.35 8.1 8.3 8.0 8.3 8.0 7.8 8.16 7.85 7.6 8.1 7.5 8.2
K.sub.2 O 2.0 2.0 1.95 1.7 1.5 2.9 3.0 2.65 1.3 3.3 3.2 3.3 3.2
3.15 3.25 3.15 3.0 3.25 3.0 3.3 P.sub.2 O.sub.5 4.3 6.25 4.1 4.25
4.15 4.15 4.15 4.2 4.1 4.2 4.1 5.2 5.0 4.9 5.1 4.0 3.85 5.1 4.7
4.15 B.sub.2 O.sub.3 2.5 2.45 2.4 2.45 2.4 2.45 2.45 2.45 2.4 1.45
-- 2.45 2.35 2.3 2.4 2.3 2.25 2.4 2.2 2.4 PbO 3.2 4.2 9.2 4.75 7.75
6.2 4.7 3.15 9.2 3.15 7.6 3.1 9.1 14.8 9.3 5.95 8.6 3.05 8.55 9.35
F 2.2 2.15 2.1 2.15 2.1 2.1 2.1 2.15 2.1 2.15 2.1 2.15 2.1 2.0 2.1
2.0 1.95 2.1 1.9 -- SrO -- -- Incls. No Few Many Few Few No No No
No No No No No No No No No No No No Opac. Dense Dense Dense Dense
Dense Very Very Poor- Poor- Poor- Poor Medium Poor Very Medium-
Dense Medium Dense Dense Poor Dense Dense Medium Medium Medium Poor
Poor Cryst. -- Apatite Apatite + Apatite -- Apatite Apatite --
Apatite + -- -- -- -- -- -- Apatite -- Apatite Apatite Apatite +
Pb.sub.3 (PO.sub.4).sub.2 Pb.sub.3 (PO.sub.4).sub.2 Pb.sub.3
(PO.sub.4).sub.2 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61
62 63 SiO.sub.2 56.7 56.6 54.9 58.5 58.1 57.2 57.0 56.6 57.6 54.0
53.1 56.15 5 5.7 57.9 57.4 56.4 54.4 56.5 59.3 Al.sub.2 O.sub.3
12.5 12.4 13.5 12.9 12.8 12.6 12.5 12.45 12.7 12.15 12.1 12.5 12.5
12.95 12.9 12.9 12.15 12.8 13.0 CaO -- 1.5 1.5 1.6 1.55 1.5 -- --
-- 1.5 1.5 1.55 1.55 1.6 1.6 1.5 1.5 1.55 1.5 BaO 4.2 5.15 6.1 4.3
-- -- 2.1 -- -- 5.9 5.9 6.1 6.1 6.3 6.3 5.9 5.9 6.25 6.15 Na.sub.2
O 8.0 8.0 7.8 8.25 8.2 8.1 8.05 8.0 8.1 7.6 7.6 7.85 7.8 8.1 8.1
8.1 7.6 8.0 7.0 K.sub.2 O 3.2 3.2 3.1 3.3 0.65 0.65 1.9 1.9 3.25
3.0 3.0 3.05 3.1 3.2 3.2 3.2 3.0 1.85 3.15 P.sub.2 O.sub.5 4.05 4.0
4.9 4.2 4.15 4.1 4.1 4.05 4.1 3.8 3.75 3.9 3.9 4.0 4.0 4.0 3.75 4.0
4.25 B.sub.2 O.sub.3 2.4 -- 2.3 2.45 2.4 2.4 2.4 2.35 2.4 2.2 2.2
2.3 2.3 2.4 2.4 2.4 2.25 2.35 2.5 PbO 9.1 9.1 5.9 3.1 9.3 9.2 9.15
9.1 6.15 8.8 8.75 6.0 6.0 3.1 3.1 3.1 8.8 6.15 3.2 F -- -- 2.0 2.15
2.1 2.1 2.1 2.05 2.1 2.0 2.0 2.05 2.05 2.1 2.1 2.1 2.0 2.1 2.2 SrO
-- -- -- 1.5 2.9 4.3 2.85 5.65 5.75 -- ZnO -- -- -- -- -- 0.55 2.1
0.6 1.1 0.6 1.15 2.25 0.55 0.6 -- As.sub.2 O.sub.3 -- -- -- -- --
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 -- Incls. No No No No No No No
No No No No No No No No No No No No Opac. Clear Poor Very Dense
Dense Dense Dense Dense Very Medium Poor- Dense Dense Dense Dense
Medium Medium Very Dense Dense Dense Medium Dense Cryst. -- --
Apatite Apatite Apatite + Apatite + Apatite Apatite + Apatite + --
-- Apatite Apatite + Apatite Apatite -- -- Apatite Apatite Pb.sub.3
(PO.sub.4).sub.2 Pb.sub.3 (PO.sub.4).sub.2 Pb.sub.3
(PO.sub.4).sub.2 Pb.sub.3 (PO.sub.4).sub.2 Pb.sub.3
(PO.sub.4).sub.2
TABLE IA
__________________________________________________________________________
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
__________________________________________________________________________
SiO.sub.2 65.2 65.2 65.2 65.2 69.5 69.5 69.5 69.5 69.3 69.5 69.5
69.5 69.5 69.5 69.5 69.5 69.5 69.6 69.5 Al.sub.2 O.sub.3 10.1 10.1
10.1 10.1 9.0 9.0 9.0 9.0 9.1 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.4
9.0 CaO 4.8 3.8 2.8 1.0 2.0 2.0 2.0 2.0 2.1 1.0 -- 2.0 1.0 -- 2.0
-- -- 2.2 2.0 BaO -- -- -- -- 3.0 3.0 3.0 3.0 3.1 3.0 3.0 2.0 1.0
-- 2.0 1.0 -- 3.0 3.0 Na.sub.2 O 9.2 9.2 9.2 9.2 9.5 9.5 9.5 9.5
9.8 9.5 2.0 9.5 9.5 9.5 9.5 9.5 9.5 9.0 9.5 K.sub.2 O 1.4 1.4 1.4
1.4 2.5 2.5 2.5 2.5 -- 2.5 9.5 2.5 2.5 2.5 2.5 2.5 2.5 -- 1.5
P.sub.2 O.sub.5 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.5 2.1 2.1
2.1 2.1 2.1 2.1 2.1 2.1 B.sub.2 O.sub.3 3.3 3.3 3.3 3.3 2.5 2.5 2.5
2.5 2.7 2.5 2.1 2.5 2.5 2.5 2.5 2.5 2.5 2.7 2.5 PbO 1.0 2.0 3.0 3.0
1.0 2.0 3.0 5.0 1.0 1.0 2.5 1.0 2.0 3.0 2.0 3.0 5.0 2.0 1.0 F 8.0
8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0
8.0 MgO 1.5 1.5 1.5 1.5 -- --
__________________________________________________________________________
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
__________________________________________________________________________
SiO.sub.2 69.5 69.5 69.5 69.5 69.5 69.5 69.5 69.5 69.5 69.5 69.5
69.5 69.5 69.5 69.5 69.5 69.0 69.0 69.0 Al.sub.2 O.sub.3 9.0 9.0
9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0
CaO 2.0 2.0 2.0 2.0 2.0 1.8 1.6 1.4 2.0 2.0 1.76 1.82 2.0 2.0 2.0
2.0 1.5 0.5 -- BaO 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 1.64
2.73 2.5 1.5 3.0 3.0 2.5 1.5 -- Na.sub.2 O 9.5 8.5 7.5
9.0 8.5 7.7 6.9 6.1 7.2 6.4 8.4 8.67 9.5 9.5 9.5 9.5 9.5 9.5 9.5
K.sub.2 O 0.5 2.5 2.5 2.0 1.5 1.5 1.5 1.5 0.5 0.5 2.2 2.28 2.0 1.5
1.0 2.5 2.5 2.5 2.5 P.sub.2 O.sub.5 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1
2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.6 2.6 2.6 B.sub.2 O.sub.3 2.5 2.5
2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 1.5 -- 2.5 2.5 2.5
PbO 2.0 1.0 2.0 1.0 2.0 1.0 2.0 3.0 1.5 2.5 2.0 1.5 1.0 3.0 1.0 2.5
1.0 3.0 5.0 F 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0
8.0 8.0 8.0 8.0 8.0 8.0
__________________________________________________________________________
39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
__________________________________________________________________________
SiO.sub.2 69.0 69.5 69.5 69.0 69.0 69.5 69.5 69.5 69.5 69.5 69.5
69.5 69.5 69.5 69.5 68.66 67.66 69.16 Al.sub.2 O.sub.3 9.0 10.0
10.5 9.5 10.5 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.1 9.1 9.1
CaO 2.0 2.0 2.0 2.0 2.0 2.0 -- 2.0 2.0 2.0 2.0 -- -- -- -- 2.02
2.02 2.02 BaO -- 3.0 3.0 3.0 3.0 -- 2.0 2.5 2.5 3.0 -- -- 1.0 -- --
2.95 2.95 2.95 Na.sub.2 O 9.5 9.5 9.5 9.5 9.5 9.5 9.5 9.5 9.5 9.5
9.5 9.5 9.5 9.5 9.5 9.37 9.37 9.37 K.sub.2 O 2.5 2.5 2.5 2.5 2.5
2.5 2.5 2.5 2.5 2.5 0.5 0.5 1.5 1.5 2.5 2.41 2.41 2.41 P.sub.2
O.sub.5 2.6 2.1 2.1 2.6 2.6 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1
2.02 2.02 2.02 B.sub.2 O.sub.3 2.5 2.5 2.5 2.5 2.5 2.5 2.5 -- 2.5
2.5 2.5 2.5 2.5 2.5 2.5 2.44 2.44 2.44 PbO 3.0 2.0 3.0 1.0 3.0 3.0
3.0 3.0 3.0 3.0 3.0 3.0 3.0 4.0 3.0 3.0 3.0 3.0 F 8.0 8.0 8.0 8.0
8.0 -- -- -- 4.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 SrO -- -- --
-- -- 3.0 3.0 3.0 3.0 3.0
4.0 -- ZnO -- -- -- -- -- 1.0 2.0 0.52 As.sub.2 O.sub.3 -- -- -- --
-- 0.036 0.036 0.036
__________________________________________________________________________
57 58 59 60 61 62 63
__________________________________________________________________________
SiO.sub.2 68.66 69.16 68.66 67.66 69.16 68.16 69.5 Al.sub.2 O.sub.3
9.1 9.1 9.1 9.1 9.1 9.1 9.0 CaO 2.02 2.02 2.02 2.02 2.02 2.02 1.88
BaO 2.95 2.95 2.95 2.95 2.95 2.95 2.82 Na.sub.2 O 9.37 9.37 9.37
9.37 9.37 9.37 7.45 K.sub.2 O 2.41 2.41 2.41 2.41 2.41 1.41 2.35
P.sub.2 O.sub.5 2.02 2.02 2.02 2.02 2.02 2.02 2.1 B.sub.2 O.sub.3
2.44 2.44 2.44 2.44 2.44 2.44 2.5 PbO 2.0 1.0 1.0 1.0 3.0 2.0 1.0 F
8.0 8.0 8.0 8.0 8.0 8.0 8.0 ZnO 1.0 0.52 1.0 2.0 0.52 0.52 --
As.sub.2 O.sub.3 0.036 0.036 0.036 0.036 0.036 0.036 --
__________________________________________________________________________
Table II records the emulsion liquidus, the high temperature
crystallization liquidus, and the low temperature crystallization
liquidus, each expressed in terms of .degree.C., determined on a
number of the exemplary compositions listed in Table I utilizing
laser reflectance measurements, along with .DELTA.T, defined as the
interval between the emulsion liquidus and the high temperature
crystalline liquidus, and a visual appraisal of the density of the
opacity exhibited by each.
Table III reports those three liquidus values, .DELTA.T, and visual
opacity appraisals for the same glasses as recited in Table II
except that PbO is absent from the compositions thereof. The
batches for the glasses (designated with an A) were compounded,
mixed, melted, poured into slabs, and the slabs annealed in like
manner to the above-described laboratory procedure.
TABLE II ______________________________________ Ex- am- Emulsion
High Temp. Low Temp. ple Liquidus Liquidus Liquidus .DELTA.T
Opacity ______________________________________ 2 1380 1315 800 65
Medium 4 1300 1210 N.O.* 90 Poor 5 1370 1310 730 60 Dense 6 1440
1380 800 60 Dense 12 1350 1275 700 75 Poor 13 1360 1300 660 60
Medium 14 1250 1200 N.O.* 50 Medium 30 1380 1315 770 65 Very Dense
31 1460 1400 880 60 Very Dense 32 1400 1320 720 80 Poor-Medium 40
1360 1305 770 55 Dense 48 1440 1390 780 50 Dense 51 1380 1300 890
80 Dense 52 1370 1300 940 70 Dense 61 1310 1230 820 80 Medium 63
1375 1315 800 60 Dense ______________________________________ *Not
Observed
TABLE III ______________________________________ Ex- am- Emulsion
High Temp. Low Temp. ple Liquidus Liquidus Liquidus .DELTA.T
Opacity ______________________________________ 2A 1380 1350 840 30
Medium 4A 1320 1290 N.O.* 30 Medium 5A 1380 1350 760 30 Dense 6A
1450 1430 820 20 Dense 12A 1360 1330 720 30 Medium 13A 1380 1350
650 30 Medium 14A 1320 1300 N.O.* 20 Medium 30A 1390 1370 800 20
Dense 31A 1390 1375 880 15 Dense 32A 1410 1390 775 20 Dense 40A
1380 1350 790 30 Dense 48A 1440 1415 800 25 Very Dense 51A 1380
1360 880 20 Dense 52A 1400 1360 900 40 Medium- Dense 61A 1320 1275
840 45 Medium 63A 1385 1360 800 25 Dense
______________________________________ *Not Observed
A comparison of Tables II and III illustrates that the inclusion of
PbO raises the value of .DELTA.T by at least 25.degree. C. and
sometimes over 50.degree. C. It has been found that values of
.DELTA.T less than 40.degree. C. generally result in the growth of
apatite inclusions during the forming process (each of the glasses
in Table III being subject thereto), accompanied with reduced
mechanical and thermal strength.
Experience has also demonstrated that the presence of PbO in
certain compositions may decrease the high temperature
crystallization temperature to such a degree that opacity is
reduced. That phenomenon is evidenced in a comparison of Examples 4
with 4A, 12 with 12A, and 32 with 32A, respectively. Although the
mechanism underlying that phenomenon has not been fully
characterized, the following explanation has been proposed. When
.DELTA.T becomes very large, the lowered glass viscosity at the
high temperature crystallization liquidus results in lower
diffusion rates for ions in the glass. That circumstance translates
into reduced crystal growth and, consequently, decreased opacity.
Increased density of opacity, however, can normally be readily
restored via minor modifications in glass composition within the
specified ranges of the constituents. The greatest opacity (without
crystalline inclusions) appears to occur when .DELTA.T is about
50.degree.-60.degree. C.
It can be observed that several of the exemplary compositions
reported in Table I exhibited some Pb.sub.3 (PO.sub.4).sub.2
crystallization. The occurrence of that crystallization is believed
to be due to low levels of CaO, SrO, and/or BaO, note, for example,
Examples 44, 49, 50, 52, and 53. The reduced quantities of those
components decreases the solubility of Pb.sub.3 (PO.sub.4).sub.2 in
the glass.
In order to determine the resistance of the inventive glasses to
detergent attack, the following tests were devised:
First, a 0.3% by weight aqueous solution of SUPER SOILAX detergent,
marketed by Economics Laboratories, St. Paul, Minn., was heated to
95.degree. C. and a sample of several of the exemplary compositions
of Table I having the dimensions of 2".times.1".times.0.25"
immersed therein for 96 hours. Table II reports the results of
those tests in terms of lead release (Pb Release) derived from
analyzing the detergent solution after the test. The standard
promulgated by the Federal Drug Administration for food contact
surfaces is a maximum lead release of 7 PPM (parts/million).
Second, a 0.3% by weight aqueous solutions of SUPER SOILAX
detergent was prepared and heated to 95.degree. C. in like manner
to the above test procedure. A sample of several of the exemplary
compositions of Table I having the dimensions of
2".times.1".times.0.25" was immersed into the solution for 96
hours, withdrawn from the solution, rinsed in tap water, and dried.
At least a portion of the sample surface was coated with SPOTCHECK
dye penetrant, marketed by Magnaflux Corporation, Chicago, Ill.,
and the dye allowed to rest thereon for 20 seconds. The dye was
thereafter dried with a clean cloth and the surface then cleaned
with a household cleansing powder for about 30 seconds. An (A)
rating in the Detergent Test signifies that no stain was observed.
A (B) rating indicates a light stain which can be removed with a
cloth wetted with detergent. Table IV reports the results of tests
conducted on several of the inventive glasses.
Also reported in Table IV are values of softening points (Soft.
Pt.) in .degree.C. where measured on several of the glasses.
TABLE IV
__________________________________________________________________________
1 2 5 6 7 9 18 19 20 21
__________________________________________________________________________
Pb Release 1.0 1.12 1.0 1.2 0.92 3.5 1.6 1.22 1.3 1.05 Detergent
Test A A A A B B A A A A Soft. Pt. -- 835 -- -- -- 810 802 785 771
810
__________________________________________________________________________
23 24 25 28 31 40 42 48 53 63
__________________________________________________________________________
Pb Release 1.3 1.0 0.85 1.0 1.1 1.25 0.90 0.84 1.6 0.92 Detergent
Test A A A A A A A A A A Soft. Pt. 811 826 818 -- 810 -- 824 782
848 785
__________________________________________________________________________
The most preferred composition is Example 63 from the standpoint of
automatic pressing processing.
* * * * *